The diabetes drugs Avandia and Actos will be labeled with severe warnings about a risk of heart failure to some patients, health officials said Tuesday.

The makers of the drugs, GlaxoSmithKline Plc and Takeda Pharmaceutical Company Ltd., have agreed to add the "black-box" warnings, the Food and Drug Administration said. The warnings, the most severe that prescription drugs can bear, stress the medicines may cause or worsen heart failure and that patients should be closely monitored.

The warnings also apply to combination drugs that include the active ingredients in Avandia, made by Glaxo, or Takeda's Actos. The drugs help patients with Type 2 diabetes control their blood sugar levels.